Compression is one of the core tools in an engineer’s arsenal. It is often used in mixes on anything from a single vocal line to an entire mix.
Compression will almost always be used in professional productions, to varying degrees. There are two main types: upward and downward compression. While the downward variant is by far more popular (and the kind of compressor beginners will learn with), both methods have their uses in day-to-day applications. Whichever option you decide to use, the end goal will always be the same: to reduce the signals’ dynamic range.
So let’s get down to it! How should you use upward & downward compression in your mix?
How to use downward compression?
We want to set the threshold where the compressor will only attenuate the sounds we want. Experiment with it a little to find the right spot. We control how much we want to reduce the signal by adjusting the ratio setting. Try starting at a 2:1 ratio, and change it according to how much you want to compress.
Generally speaking, you should set the attack and release parameters so that the compression sounds natural (no audible artifacts). You can use abnormally fast or slow attack/release times, depending on whether or not you like the way they affect the sound. For example, you might want to use a slower release time to sustain long notes in a piano piece.
With infrequent overly loud sections, downward compression will be more effective than upward when most of your recording is appropriately loud. Upward compression will be more effective when most of the recording is loud enough but has occasional soft parts.
- Downward compression is more effective for occasional loud sounds.
- Upward compression is more effective for infrequent soft sounds.
Try not to confuse loudness with level. If you’re struggling to hear a sound in your mix, turn its level up before deciding whether or not to use compression.
Different settings for different genres
The genre of music will help you determine how much compression you should be using (if used at all). Commercial/Electronic music relies heavily on compression for competitive loudness, while acoustic/classical music relies on a wide dynamic range instead.
With that said, you can use compression on classical music or even refrain from using it at all when producing electronic music. There are no rules, only what sounds good and what doesn’t.
How does downward compression work?
Downward compression attenuates all sounds above the threshold by a set ratio. The higher the ratio, the more the audio is reduced. Put plainly, downward compression makes the loudest sounds quieter and leaves the softer sounds in the recording untouched. Most compressors will have basic controls you can tweak to taste. These will affect the sound in different ways explained below.
The threshold determines when the compressor will start working. Any audio above it will be compressed, and any sounds below it will be unaffected.
The attack controls the speed at which the compressor will start working (typically expressed in milliseconds or ms). Setting this too low might compromise any intended transients, while setting it too high (in combination with an aggressive threshold setting) might create unintended transients.
This parameter controls how quickly the compressor returns to its idle state (also in ms).
The ratio determines how much of the signal is attenuated. So at a setting of 2:1, all audio above the threshold will be reduced by half its original loudness.
This setting is used to regain any level/volume lost during compression. Sometimes called makeup-gain, it’s handy for A/B testing when listening for the differences between the compressed and uncompressed signal. Remember, it is crucial to A/B test with the processed and unprocessed signal at the same level/volume.
Note that not all compressors are the same, and some of these settings might be absent or controlled automatically.
Figure A: Downward compression.
There is a fine line between well-compressed and overcompressed audio. Overcompression can lead to unnatural sounding pumping or breathing in a mix. Setting the ratio too high, setting the threshold too low, or even setting the attack or release too fast/slow, can ruin your recording. Therefore it is crucial to be conservative.
That being said, overcompression is desirable in some cases, so a little bit of experimentation will help you decide how to compress your audio.
Remember that all audio is different, and there is no “one size fits all” approach to compression.
How to use upward compression?
Upward compressors generally have the same adjustable parameters as downward compressors. However, there are a few key differences in how the compressor works. Most notably is the threshold setting. It works oppositely from a downward compressor.
We want to set the threshold above the sounds we want to boost but simultaneously below the louder sounds. As with downward compression determining the correct settings requires a little experimentation.
How does upward compression work?
Upward compression (Not to be confused with expansion, which is used to increase the dynamic range of a signal or recording) makes the quietest sounds louder. It achieves this by increasing the audio level below the threshold by a set ratio.
As stated, a few settings work differently from downward compressors.
While this setting still determines when the compressor will start working, the signal below the threshold increases in volume instead. Any audio above the threshold is left untouched.
With upward compression, the ratio determines how much the signal is boosted. So at a ratio of 0.5:1, everything below the threshold is doubled in level. Going higher than 1:1, however, means downward compression will occur instead.
Figure B: Upward compression.
Why use compression?
The main reason to use compression is to reduce a sound’s dynamic range. We do this so that we can then make the overall sound louder. The human ear responds to average level rather than ‘peak’ level. How our ears perceive sound is why things generally sound better when more audible.
Figure C: Dynamic range is the difference between the loudest and softest parts of a signal.
Today, loudness is crucial in creating a competitive product in the music industry. Ideally, we would never have to compress the life out of our mixes to have them competitively loud. Using compression effectively is therefore essential for both aspiring and established sound engineers. It is one of the processes you can’t neglect in your journey to becoming a well-rounded sound engineer.
Hopefully, after reading this article, you will know how to compress sensibly and which type of compressor you should use.
Shaurya Bhatia, is an Indian Music Producer, Composer, Rapper & Performer, who goes by the stage name MC SNUB, and is also 1/2 of the Indian pop music duo, called “babyface”. A certified Audio Engineer & Music Producer, and a practicing musician & rapper for more than 6 years, Shaurya has worked on projects of various genres and has also been a teaching faculty at Spin Gurus DJ Academy.